In mobile broadband, studies have shown that subscribers use the internet in a similar manner to fixed broadband. Users often use the mobile broadband for applications such as gaming or Voice-over-Internet-Protocol (VoIP) applications.
FIG. 1 shows some of the basic components of a telecommunications network, known as the UTRAN (UMTS, Universal Mobile Telecommunications System, Terrestrial Radio Access Network). The network comprises a plurality of Radio Base Stations (RBSs) 11, each of which maintains one or more cells (not illustrated). User Equipment 13 (“UE”, i.e. mobile equipment or mobile nodes) within each cell communicate with the corresponding RBS 11 of that cell. A Radio Network Controller (RNC) 15 is provided for controlling several RBSs 11.
A Serving Gateway (SGW) 17 may be connected to one or more RBSs 11, plus other nodes such as serving General Packet Radio Service (GPRS) Support Nodes (SGSNs, not shown). The SGW 17 is connected to a Packet data network GateWay (P-GW) 19. The P-GW 19 provides connectivity between the user equipment 13 and external packet data networks, such as the internet 21, by being the point of exit and entry of traffic for the user equipment.
In a network such as that described in FIG. 1, a User Equipment 13 and RBS 11 communicate by means of several different types of communication channel.
For example, in UTRAN logical channels, transport channels and physical channels exist. The logical and transport channels define what data is transported, while the physical channels define how, and with what physical characteristics, the data is transmitted.
Transport channels can be further subdivided into common transport channels and dedicated transport channels.
The common transport channel types include, amongst others, a Random Access Channel (RACH) and a Forward Access Channel (FACH). The RACH is a contention based uplink channel used for transmission of relatively small amounts of data, for example for initial access or non-real-time control or traffic data. The FACH is a common downlink channel which, as with the RACH, is only used for transmission of relatively small amounts of traffic data.
A dedicated transport channel, on the other hand, is a channel dedicated to one User Equipment for uplink and/or downlink transmissions.
In such a telecommunications network the transmitted user data is monitored, for example in a Serving Radio Network Controller (S-RNC), and evaluated to determine whether a channel switching operation should be performed from a dedicated transport channel to a common transport channel. For example, if user throughput decreases such that a switch from a dedicated transport channel to a common transport channel (e.g. FACH/RACH) is required, a down-switch request is sent to trigger a channel switching operation.
FIG. 2 shows an example of a channel switching operation between a dedicated transport channel and a common transport channel. When the throughput on the uplink and downlink falls below a first threshold value (Threshold-1) at time t1 a timer is started. If the throughput increases above a second threshold value (Threshold-2) before the timer expires (for example as shown at point t2), the timer is stopped and no channel switching operation is performed. However, when throughput on the uplink and downlink falls below the first threshold value (Threshold-1) at time t3 and the timer started, if the throughput is still below the second threshold (Threshold-2) when the timer expires (for example as shown at point t4), then a channel switching operation is triggered, i.e. from a dedicated transport channel to a common transport channel. The evaluation can be restarted when the channel switching request is issued, so that any failures during the channel switching can be detected (i.e. if the channel switch fails, a new request is issued when the restarted timer expires). The use of first and second thresholds and a timer in the example above is provided for stability reasons, and helps in preventing switching back and forth at momentary dips in throughput.
While the switching from a dedicated transport channel to a common transport channel can be advantageous in so far as any unused network resources are seized back from the user, such channel switching can be problematic in certain applications. For example, in gaming or VoIP applications the time taken to regain access to a dedicated transport channel can cause problems.
Furthermore, if a user wishes to play an online game, such as a quick action shooting game, the round trip time (RTT) of the communication link is critical in such fast pace games. A 100 ms latency will cause noticeable user experience degradation, while a 300 ms latency can make such games unplayable. One way for a user to avoid this problem is to select a server that provides the desired RTT in order to give the user an acceptable perceived quality. The RTT measurement is usually carried out by sending a plurality of data packets (also known as ping packets) towards various servers and measuring the response times, such that a server having an acceptable RTT can be selected. However, since the throughput for such ping packets is quite small, the radio link is capable of serving such ping packets on the common transport channel (i.e. RACH-FACH), which gives misleading information about the network quality to the user.
In addition, to prevent cheating several gaming applications do not allow users to join via servers having an RTT above 200 ms, since a RTT above 200 ms can be a potential risk in so far as it provides enough time for manipulating the gaming packets in real time by a third party software. Such applications do not allow players to join even if the channel switching to dedicated transport channel would eliminate the high RTT problem.
Other applications such as VoIP apply silence detection to lower the total data cost of the communication during long pauses in the data transmission. The pause in the data transmission can cause the transmitting buffers to become empty, which in turn causes the user equipment to switch from a dedicated transport channel back to a common transport channel (a RACH-FACH channel). These common transport channels do not usually provide enough capability to fulfil the requirements necessary for a good VoIP session, thus a channel switching operation back to the dedicated transport channel usually occurs when conversation is restarted after a silence period. This results in bursty packet delivery and poor voice quality.